1. FIELD OF THE INVENTION
The present invention pertains to a communication system for a helicopter which allows access to relay data-containing information carried by radiowaves transmitted from fixed stations on the ground or from mobile stations such as flying vehicles.
2. DESCRIPTION OF THE RELATED ART
It often occurs that one partner in a telecommunication operation happens to be an aircraft. Helicopter relay systems have utilized in the broadcasting industry, for gaining access to information in a real-time manner which is gathered in a remote place.
In such a relay system, images gathered on the ground are first received through a microwave transit trunk by a helicopter, and then are re-transmitted by the helicopter to a base station.
To realize the above-mentioned relay system, first, a helicopter must be near enough to a transmitting source on the ground to allow stable communication. Second, it is desirable to employ a directional antenna for better reception. In this case, however, it is necessary to first gain information regarding the direction of the communication partner in order to point the directional antenna in the appropriate direction.
In both of these cases, it is necessary for a helicopter to determine the direction of the transmitting source.
As regards the former method, i.e., contacting a transmitting source, two methods have been conventionally utilized: A first method has the helicopter approach the transmitting source with the help of navigation machinery aboard the helicopter, while information is exchanged on the location of the helicopter and the transmitting source. This exchange of information is carried out by voice communication assisted by different communication lines before or during flight. A second method has the helicopter approach the transmitting source, while signs on the ground are detected by vision.
Unfortunately, however, adjusting a direction antenna appropriately in the direction of a communication partner demands information on the direction of the partner which is much more accurate and reliable than that required for the above-mentioned methods of contacting the transmitting source. For this reason, realizing these methods involves a number of difficulties in terms of accuracy.
In the first method, for, contacting the transmitting source, the flight direction is determined based on information obtained from the navigation gear together with reference to a map. This operation is troublesome to the pilot, and furthermore the information on the direction of the transmitting source is inaccurate. It may be practically impossible to adapt this method to particularly small helicopters, since the number of crew members is limited. Further, in the second method, i.e., relying on human vision, the success of the method depends upon weather conditions, and thus it may be impossible to contact or locate the transmitting source due to poor visibility.
When communication and its relay are performed by using a conventional helicopter, a problem exists in that the full relay capability inherent in the use of the aircraft is not utilized due an inability to effectively determine of with sufficient accuracy and reliability, the direction of the communication partner during flight.